Biological Charcteristics Of Endophytic Bacterium Strain B₄₇ And Its Biocontrol To Tomato Bacterial Wilt

Tomato bacterial wilt is one of the most important plant soilborne diseases. It is very difficult to control this disease. The endophytic bacterium strain B₄₇ which was isolated from the stem of tomato, could strongly inhibit the growth of Ralstonia solanacearum. The biological characteristics of strain B₄₇ and its biocontrol effect on tomato bacterial wilt were studied in this research, the results of experiments as follows:Strain B₄₇ was identified as Bacillus subtilis according to the investigation of morphology, test of physiological and biochemical characteristics and analysis of 16S rDNA sequence. For the growth of the strain, the optimum pH and temperature were 5.8 and 35℃, respectively. It could use many carbons as carbon source and organic nitrogen as nitrogen source.Entry the plants tissue of tomato for strain B₄₇ was tested by means of dipping seed, dipping root, watering root, spray, injecting stem, puncturing stem and puncturing leaf. The results showed that strain B₄₇ could penetrate the tissue of tomato through wounds. Under the microscope, strain B₄₇ could be seen in the vessels and cells of tomato stems. And strain B₄₇ could colonize in 7 varieties of tomato, this results indicated that the strain might not select varieties to live in.Soil microbes affected the colonization ability of strain B₄₇ in plants. The population of strain B₄₇, which was from the roots and stems of plants cultivated in steam-sterilized soil was larger than that of plants cultivated in raw soil. The experiment indicated that soil microbes could indirectly affect the viability in plants. Meanwhile, growth period of plant could also affect thecolonization ability of strain B₄₇ in plants. The number of the strain increased from seedling to fruit stage, and then decreased after fruit stage. This result indicated that the colonization ability of strain B₄₇ in plants was related to the physiological and biochemical activities of plants.There was difference in development rate in plants between strain B₄₇ and Ralstonia solanacearum. The development rate of strain B₄₇ was slowlier than that of Ralstonia solanacearum. When strain B₄₇ was used to control tomato bacterial wilt, 81.25% of control effect could be obtained when strain B₄₇ was inoculated to tomato earlier than Ralstonia solanacearum. If strain B₄₇ and Ralstonia solanacearum were inoculated to tomato simultaneously, the strain B₄₇ could not effectively control the disease. Furthermore, the control effect of mixture of B₄₇ and St₁₀₃ was evidently higher than that of strain B₄₇ or strain St₁₀₃.The results of field control test also indicated that the mixture of B₄₇ and St₁₀₃ could effectively control tomato bacterial wilt in bloom period. The control effect was 81.82%. But it fell to 30.91% in the later of tomato growth period.